The major semiconductor devices for integrated circuits (ICs), especially in very-large scale integrated (VLSI) circuits, include metal-oxide-semiconductor field-effect transistors (MOSFETs). With the continuous development of IC manufacturing technology, the technical nodes of semiconductor devices continue to decrease, and the geometrical dimensions of semiconductor devices become smaller and smaller following the Moore's law. When the reduction of the dimensions of semiconductor devices reaches a certain level, various secondary effects due to approaching to the physical limits of semiconductor devices begin to emerge, and thus further scaling down the feature size of semiconductor devices becomes more and more difficult. Among all the problems in the field of semiconductor manufacturing, the most challenging one is to solve the large leakage current issue in semiconductor devices. Specifically, a large leakage current in a semiconductor device is mainly caused by the continuous decrease in the thickness of the conventional dielectric layer in the semiconductor devices.
Conventional solutions include use of a high-k material to replace the commonly-used SiO2 as the gate dielectric material and also use a metal material as the gate electrode material to avoid Fermi level pinning between the high-k material and the conventional gate electrode material and also avoid boron penetration. Such a gate structure using a high-k material to form the gate dielectric layer and a metal material to form the gate electrode is known as a high-k metal gate (HKMG). The introduction of the HKMG reduces the leakage current in semiconductor structures.
Although the introduction of the HKMG may have improved the electrical performance of semiconductor devices to a certain extent, the electrical performance of existing semiconductor devices may still need to be improved. The disclosed semiconductor structures and fabrication methods thereof are directed to solve one or more problems set forth above and other problems in the art.